ci: introducing cncf/prow-github-actions (#3536)

Signed-off-by: Jan Larwig <jan@larwig.com>

CONTRIBUTING.md

@@ -1,26 +1,113 @@
 # Contributing
 
-To develop on this project, please fork the repo and clone into your `$GOPATH`.
+Thank you for contributing to OAuth2 Proxy. We track bugs, feature requests,
+and other work in GitHub issues. Please follow the issue and pull request
+templates, including their checkboxes.
 
-Dependencies are **not** checked in so please download those separately.
-Download the dependencies using `go mod download`.
+## Development setup
+
+Fork the repository, clone your fork, create a feature branch, and download Go
+dependencies:
 
 ```bash
-cd $GOPATH/src/github.com # Create this directory if it doesn't exist
-git clone git@github.com:<YOUR_FORK>/oauth2-proxy oauth2-proxy/oauth2-proxy
-cd oauth2-proxy/oauth2-proxy
+git clone git@github.com:<YOUR_FORK>/oauth2-proxy.git
+cd oauth2-proxy
+git switch -c feature/<BRANCH_NAME>
 go mod download
 ```
 
-## Pull Requests and Issues
+Install the Go version declared in the repository's `go.mod`. The
+[Go installation guide](https://go.dev/doc/install) and
+[Go downloads page](https://go.dev/dl/) explain how to install a specific
+release.
 
-We track bugs and issues using Github.
+We suggest [Visual Studio Code](https://code.visualstudio.com/docs/languages/go)
+with the official
+[Go extension](https://marketplace.visualstudio.com/items?itemName=golang.go).
 
-If you find a bug, please open an Issue.
+### Local testing and debugging
 
-If you want to fix a bug, please fork, create a feature branch, fix the bug and
-open a PR back to this repo.
-Please mention the open bug issue number within your PR if applicable.
+To run OAuth2 Proxy locally with an example upstream and identity provider,
+use the Makefile in `contrib/local-environment`:
+
+```bash
+cd contrib/local-environment
+make up
+```
+
+Other available environments include:
+
+- Dex with alpha config: `make alpha-config-up`
+- Keycloak: `make keycloak-up`
+- Dex with nginx: `make nginx-up`
+
+See that Makefile for the complete set of environments and their corresponding
+tear-down commands. The default local credentials are usually
+`admin@example.com` and `password`.
+
+The environments use `localtest.me`:
+
+- OAuth2 Proxy: <http://oauth2-proxy.localtest.me:4180>
+- Upstream: <http://httpbin.localtest.me:8080>
+- Dex: <http://dex.localtest.me:5556>
+
+For VS Code debugging, create `.vscode/launch.json` from the "Run and Debug"
+view and use `Go: Launch Package`. The following configurations start OAuth2
+Proxy with the local Dex or Keycloak environments:
+
+```jsonc
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Launch OAuth2 Proxy with Dex",
+      "type": "go",
+      "request": "launch",
+      "mode": "auto",
+      "program": "${workspaceFolder}",
+      "args": [
+        "--config",
+        "contrib/local-environment/oauth2-proxy.cfg"
+      ]
+    },
+    {
+      "name": "Launch OAuth2 Proxy with Keycloak",
+      "type": "go",
+      "request": "launch",
+      "mode": "auto",
+      "program": "${workspaceFolder}",
+      "args": [
+        "--config",
+        "contrib/local-environment/oauth2-proxy-keycloak.cfg"
+      ]
+    }
+  ]
+}
+```
+
+## Pull requests and issues
+
+If you find a bug, open an issue. To fix a bug, create a feature branch, make
+the change, and open a pull request against this repository. Mention the
+related issue number in the pull request when applicable.
+
+GitHub's required reviews and CODEOWNERS rules are the authoritative merge
+approval process. Reviewers should use GitHub's native review interface to
+approve changes.
+
+### GitHub commands
+
+Prow-style commands may be posted as their own line in issue and pull request
+comments:
+
+- `/assign` and `/unassign` assign or unassign users.
+- `/area`, `/kind`, and `/provider` apply a configured classification label.
+- `/help` adds the `help wanted` label.
+
+On pull requests only, project reviewers may also use `/lgtm` and
+`/lgtm cancel` to manage the review-readiness label. A new commit removes the
+`lgtm` label. The label does not merge a pull request or replace GitHub
+approval requirements.
 
 ## AI use